Tire tread patterns are provided in a tire tread from the objective of improving running performance in rain. Because most tire tread patterns have grooves that extend in circumferential and widthwise directions of the tire, land portions called blocks are formed in the tread.
However, it is known that pattern noise is generated because the blocks are provided.
Conventional technology concerning overcoming pattern noise can be largely categorized into two types.
The first type is a method in which the angle of lug grooves with respect to the tire widthwise direction is increased, in order to extend the time during which input is applied to a single block.
The second type is a method in which peaks are not given to a single frequency, by utilizing the relation with other blocks, for example, by varying the circumferential-direction lengths of the blocks or shifting phases within the same tire tread.
These technologies were mainly developed on the basis of two-dimensional conception, and their history is long.
However, with respect to automobiles in recent years in which quietness has been sought, the effects of the aforementioned conventional technology have not been sufficient. Moreover, because designs that place importance only on noise reduction using the aforementioned methods are not realistic in view of balance with other characteristics, new technology is in demand.
Particularly with respect to a single block, it has been reported that, when the angle of the lug grooves with respect to the widthwise direction of the tire is increased (i.e., when the pattern design is changed), block rigidity deteriorates as the configuration of the block becomes similar to a parallelogram which is long and thin in the circumferential direction. Further, in this case, partial wear is likely to occur.
In view of the above facts, it is an object of the present invention to provide a pneumatic tire in which noise can be reduced without changing the basic design of the block pattern.